Telechelic polymers are polymers that contain two functional groups per molecule at the termini of the polymer. Such polymers have found wide utility in many applications. For instance, telechelic polymers have been employed as rocket fuel binders, in coatings and sealants and in adhesives. In addition, polymers that contain two hydroxyl groups per molecule can be co-polymerized with appropriate materials to form polyesters, polycarbonates, and polyamides (see U.S. Pat. No. 4,994,526).
A variety of polymerization techniques, such as cationic and free radical polymerizations, have been employed to prepare telechelic polymers. However, functionality can be best controlled with anionic polymerization. An early approach to the preparation of telechelic polymers is described in D. N. Schulz, et al, J. Polym. Sci., Polym. Chem. Ed. 12, 153 (1974), which describes the reaction of a protected hydroxy initiator with butadiene. The resultant living anion was quenched with ethylene oxide to afford mono-protected di-hydroxy polybutadiene. While excellent functionality (f=1.87-2.02) was achieved by this process, the protected initiator was insoluble in hydrocarbon solution. Therefore, the reaction was conducted in diethyl ether, and as a result, relatively high 1,2 microstructure (31-54%) was obtained.
Another approach that has been employed to prepare telechelic polymers is the generation and subsequent functionalization of a "dilithium initiator". A dilithium initiator is prepared by the addition of two equivalents of secondary butyllithium to meta-diisopropenylbenzene. The dilithium initiator is then reacted with a conjugated diene, such as butadiene or isoprene, to form a polymer chain with two anionic sites. The resultant polymer chain is then reacted with two equivalents of a functionalizing agent, such as ethylene oxide. While useful, gelation is frequently observed during the functionalization step. This leads to lower capping efficiency (see, for example, U.S. Pat. No. 5,393,843, Example 1, wherein the capping efficiency was only 82%). Additional details of this gelation phenomenon are described in U.S. Pat. No. 5,478,899. Further, this dilithium approach can only afford telechelic polymers with the same functional group on each end of the polymer chain.
Great Britain published patent application 2,241,239, published Aug. 28, 1991, describes a novel approach for producing telechelic polymers in hydrocarbon solution. Telechelic polymers were prepared using monofunctional silyl ether initiators containing alkali metal end groups that were soluble in hydrocarbon solutions. These monofunctional silyl ether initiators were demonstrated to be useful in producing dihydroxy (telechelic) polybutadienes having desirable characteristics, such as a molecular weight of typically 1,000 to 10,000, a 1,4 microstructure content of typically 90%, and the like.